1. Field of the Invention
The present invention relates to a development apparatus in which a development process is carried out in such a manner that a non-magnetic one-component type developer comprising matrix toner particles and an auxiliary component is supplied to a developer-bearing-member which is driven in rotation, the developer on the developer-bearing-member is transported to a development area where the development-bearing-member and a latent-electrostatic-image-bearing member face each other, and the latent electrostatic images formed on the latent-electrostatic-image-bearing member are developed to visible toner images by the above-mentioned developer.
2. Discussion of the Background
An image forming machine such as an electrophotographic copier, printer or facsimile machine commonly employs a dry-type development apparatus in which latent electrostatic images formed on a latent-electrostatic-image-bearing member are developed to visible toner images by use of a dry-type developer to obtain recorded images.
The conventional dry-type developer is divided into two groups; a two-component developer comprising a toner and a carrier, and a one-component developer comprising a toner. Although the two-component developer can produce relatively stable recorded images, it has the shortcoming that the carrier component easily deteriorates, causing the mixing ratio of the toner component to the carrier component to easily vary. Therefore, maintenance and control of the development apparatus employing the two-component developer become complicated, and consequently, it is difficult to make the development apparatus compact in size.
With these shortcomings of the two-component developer taken into consideration, attention has been paid to the one-component developer. Two kinds of one-component developers are conventionally known, one comprises toner particles, and the other comprises toner particles and an auxiliary component. The auxiliary component is, for example, a fluidity-imparting agent capable of improving the fluidity of the toner particles.
In a development apparatus employing the one-component developer, the one-component developer supplied to a developer-bearing-member is transported to a development area where the developer-bearing-member and a latent-electrostatic-image-bearing member face each other, and the latent electrostatic images formed on the latent-electrostatic-image-bearing member are developed to visible toner images by the one-component developer. To form high-quality toner images with a predetermined image density on the latent-electrostatic-image-bearing member, it is necessary to transport a large quantity of the toner which is sufficiently charged to a preset polarity to the development area.
The optimal deposition amount and charge quantity of a non-magnetic one-component type developer will now be explained in detail.
In the formation of black and white images, the charge quantity of toner, to which great importance is attached, is generally in the range from 5 to 20 .mu.C/g. When the charge quantity of the toner is less than the above-mentioned range, the obtained image quality becomes poor because of toner deposition on the background and insufficient sharpness of the obtained images. The deposition amount of the toner on the developer-bearing member such as a development roller is generally in the range of 0.1 to 0.3 mg/cm.sup.2. On the other hand, the required deposition amount of toner on a sheet of image-receiving paper is 0.8 to 1.0 mg/cm.sup.2. To satisfy the above-mentioned toner deposition amount on the image-receiving sheet, the rotational speed of the development roller is set three to four times that of the latent-electrostatic-image-bearing member such as a photoconductor. When the development roller is rotated as fast as previously mentioned, however, only the end portion of a solid black image shows an increased image density. The above phenomenon can be eliminated by approximating the rotational speed of the development roller to that of the photoconductor. Consequently, it is desirable to decrease the rotational speed of the development roller, and at the same time, to increase the toner deposition amount on the development roller.
When the one-component developer comprising the matrix toner particles and the fluidity-imparting agent is used in the development apparatus, the above-mentioned desired charge quantity and deposition amount of the toner on the development roller cannot be obtained because the triboelectric charging of the toner cannot be increased. There is an increasing demand for a development apparatus in which an appropriate charge quantity of the toner and a proper toner deposition amount on the development roller can be obtained even though the one-component type developer comprising the matrix toner particles and the fluidity-imparting agent is used therein.